Ferromagnetic materials with low coefficient of temperature of the initial magnetic permeability



C. GUILLAUD Feb. 13, 1962 FERROMAGNETIC MATERIALS WITH LOW COEFFICIENT OF TEMPERATURE OF THE INITIAL MAGNETIC PERMEABILITY 2 Sheets-Sheet 1 Filed Jan. 5, 1958 Inventor c. GU/[LA UD Q/M. mffi Attorney Feb. 13, 1962 c. GUILLAUD 3,021,283 FERROMAGNETIC MATERIALS WITH LOW COEFFICIENT OF TEMPERATURE OF THE INITIAL MAGNETIC PERMEABILITY Filed Jan. 3, 1958 2 Sheets-Sheet 2 OT 0N Oh Q RNQ oaw t o a No NdE 00% OOR 00m 08 009 o o: 00% 002 003 Inventor CCU/[1A UD QA )4. 44 Attorney United States Patent 3,021,283 FERROMAGNETIC MATERIALS WITH LOW C0- EFFICIENT 0F TEMPERATURE OF THE INITIAL MAGNETIC PERMEABELITY Charles Guillaud, Bellevue, France, assrgnorfo Centre National de la Recherche Scientifique, Paris, France, a corporation of France Filed Jan. 3, 1958, Bar. No. 707,049 Claims priority, application France Jan. 8, 1957 2 Claims. (Cl. 252-4525) The invention relates to ferromagnetic materials vwith low temperature coefificient of the initial permeability, said materials consisting of solid homogeneous solutions of metallic oxides comprising oxides of iron Fe O and FeO, the latter oxide not necessarily being present, of nickel oxide NiO, Zinc oxide ZnO, aluminum oxide A1 0 chromium oxide Cr O the two latter oxides may be together or separately.

It is known that these materials are prepared, generally speaking, by subjecting to a heat treatment a pulverulent mixture comprising the above-mentioned oxides previously agglomerated under pressure to the desired form.

The invention also relates to a. method of manufacturing said materials.

In order to permit a better understanding of the following, we will first of all define an essential characteristic of the materials concerned.

It is known that the initial magnetic permeability of ferromagnetic materials varies more or less as a function of the temperature. The amplitude of this variation is conveniently expressed by a magnitude known as coeflicient of temperature of the initial magnetic permeability. This coefiicient will hereinafter be described by u By this term is meant the difierence between the maximum intial (;r max.) and minimum (--,a min.) magnetic permeabilities marked in a given temperature interval t and t this difference being divided by the product of the initial magnetic permeability (,u measured at 0 C. and the difference between the limit temperatures of this interval:

1 max. min. oeu= It is also possible to give this coefficient in percent per degrees centigrade (this numerical value then being the centuple of that corresponding to the above formula).

For certain practical applications, the coeflicients of temperature or" the initial magnetic permeability must be very low and this within a large temperature interval. Thus, materials having the same composition of oxide of nickel and zinc as those which will be specified in the following, but of which the oxides of aluminum and chromium have been replaced by oxide of iron, cannot be used owing to the fact that the amplitude of variation of the initial magnetic permeability is too high.

The object of the present invention is to give the compositions and the methods of manufacture making it possible to obtain materials having low coefficients of temperature of the initial magnetic permeability in temperature intervals which may exceed 100 C., While maintaining their magnetic permeability sufiiciently high.

For this purpose a. starting mixture of oxides of iron, aluminum, chromium, nickel and zinc is prepared, comprising in molecular percentage: 33% to 50% of iron oxide l e- 0 16% to 23% of nickel oxide, 1% to 15% of aluminum or chromium oxide or of the total of these two latter oxides, the remainder being zinc oxide ZnO. This mixture, after grinding in a ball mill, usually of steel, is agglomerated under pressure in the form desired. The agglomeration thus obtained is then sintered at a temperature between l,100 and 1,350 C., in an oxidizing atmosphere for a time usually spread out between 2 and 4 hours, preferably at 1,2S0 C. in an atmosphere of pure oxygen for 4 hours.

As has been indicated, the percentages of oxide of aluminum A1 0 or oxide of chromium Cr O or again of aluminum oxide A1 0 and chromium oxide Cr O may vary within certain limits. They must be determined as a function of the molecular content of nickel-oxide NiO and of the heat treatment, in such a way that in a temperature interval of at least 50 C., situated between 40 and C., the value of the coefficient of temperature of the initial magnetic permeability of the material is less than half the value of the same coefiicient measured on a material which has been subjected to the same heat treatment and having the same composition, apart from the fact that the whole of the oxides of chromium and aluminum are replaced by an identical molecular percentage of iron oxide Fe O In the foregoing, it has been assumed for purposes of simplification in expressing the molecular percentages, that the metals were in the starting mixture solely in the form of oxides of iron Fe O oxide of nickel NiO, oxide of aluminum A1 0 oxide of chromium Cr O and zinc oxide ZnO. They could, however, equally well appear in another form, for example, in the form of other oxides or in the form of salts, in which case it would be suflicient to convert the other oxides, metals or salts really present in the above indicated oxides to equality of the number of metallic atoms.

In any case, the invention will be better understood by means of the following non-limitative examples and the attached drawings.

FIG. 1 shows the variation, as a function of the temperature, of the initial magnetic permeability of the materials produced in accordance with the invention, prepared from diilerent starting mixtures all comprising 50% mol. for the combination (Fe O -A1 O 18% mol. of NiO, the remainder consisting of ZnO. The various curves represented each correspond to a particular percentage of oxide A1 0 which percentage varies from 0 to 10% mol. which has been indicated on the corresponding curve. It is possible to observe how the action of the oxide Al O is important on the value of up, in particular with 7% of A1203 and, consequently, 43% of Fe O a very low can is obtained.

FIG. 2 relates to materials comprising 50% mol. for the combination (Fe O Al O 20 mol. of NiO, the remainder consisting of ZnO. Each curve relates to a particular content of oxide A1 0 these contents spreading from 0 to 15% mol. of A1 0 For a content of 10% of A1 0 the value of up. is very low.

In order to plot the curves represented on FIGS. 1 and 2 and to facilitate comparison, the initial magnetic permeability has, in each case, been conventionally reduced to the value 1,000 at 0 C., by multiplying the real value by a suitable numerical coefiicient. The initial magnetic permeability at the other temperatures have been multiplied by the same coefiicient.

Unless otherwise indicated in the following examples, the ferromagnetic materials have been prepared by mixing together the oxides in the molecular proportions indicated, by grinding in an aqueous medium by means of a steel ball mill for 24 hours, then drying and compressing in the form of a toroid under a pressure of 5 tons/cm?- Example 1 An initial mixture is prepared, containing in molecular proportions: 18% of NiO, 43% of F6 0 7% of A1 0 the remainder ZnO. The heat treatment of the stamped product is efiected at 1,250 C. in oxygen for 4 hours and the period of cooling is 15 hours. The coefiicient of temperatureof the initial permeability measured on one toroid is .05 per degree centigrade in the interval 40 to +80 C. The coefiicient of temperature prepared under the same conditions from a starting mixture containing in molecular proportions 50% of Fe O 18% of NiO and the remainder of ZnO is 1.2% per degree centigrade in the temperature interval specified hereinabove.

Example 2 A mixture is prepared containing in molecular proportions 20% of NiO, 40% of Fe O 10% of A1 the remainder being of ZnO. After heat treatment at 1,250 C. for 4 hours in an oxygen atmosphere and cooling for 16 hours, the co'eificient of temperature of the initial permeability measured on a toroid is 0.06% per degree centigrade in the interval 40 to +80 (1, While this coefiicient measured on a toroid obtained from an initial mixture containing 20% of N10, 50% of Fe O the remainder ZnO, and subjected to the same heat treatments as above is 0.9% per degree centigrade in the interval 40 to +80 C.

Example 3 Starting with a mixture containing in molecular proportions: 20% of NiO, 10% of Cr O 40% of Fe O Example 4 a From a starting mixture containing in molecular proportions: 19% of NiO, 5% of A1 0 5% of Cr 0 39.7% of Fe O the remainder being of ZnO, a material is prepared using the same heattreatments as those given in Example 1. The coeflicient of temperature of the initial permeability of this material in the interval 40 to +80 C. is 0.07% per degree centigrade.

What I claim is:

1. A ferromagnetic ceramic material with a temperature coeificient of initial permeability over a temperature range of at least C. between 40 C. and C. less than a nickel-Zinc ferrite over the same temperature range, comprising the reaction product formed by compressing a mixture of 33-50 mol. percent Fe O 16 to 20 mol. percent NiO, containing 5 to 15 mol. percent of a mixture of A1 0 and Cr 0 with the Cr O being at least 5 mol. percent and the remainder ZnO, and heating the compressed mixture in an oxygen atmosphere at a temperature between 1100" C. and 1350 C. for from two to four hours.

2. A ferromagnetic ceramic material having a coefiicient 'of temperature of the initial permeability of approximately 0.07% per degree centigrade over a temperature range of 4( C. to +80 C., comprising the reaction product formed by compressing and heat treating in an oxygen atmosphere at l250 C. for 4 hours, a mixture of 39.7 mol. percent Fe O 19 mol. percent NiO, 5 mol. percent A1 0 5 mol. percent Cr O and the remainder ZnO.

References Cited in the file of this patent UNITED STATES PATENTS Leverenz et al. Aug. 28, 1951 

1. A FERROMAGNETIC CERAMIC MATERIAL WITH A TEMJPERATURE COEFFICIENT OF INITIAL PERMEABILITY OVER A TEMPERATURE RANGE OF AT LEAST 50* C. BETWEEN -40*C. AND +80*C. LESS THAN A NICKEL-ZINC FERRITE OVER THE SAME TEMPERATURE RANGE, COMPRISING THE REACTION PRODUCT FORMED BY COMPRESSING A MIXTURE OF 33-50 MOL. PERCENT FE2O3, 16 TO 20 MOL. PERCENT NIO, CONTAINING 5 TO MOL. PERCENT OF A MIXTURE OF AL203 AND CR203 WITH THE CR203 BEING AT LEAST 5 MOL. PERCENT AND THE REMAINER ZNO, AND HEATING THE COMPRESSED MIXTURE IN AN OXYGEN ATMOSPHERE AT A TEMPERATURE BETWEEN 1100*C. AND 1350*C. FOR FROM TWO TO FOUR HOURS. 